How Does A Narrow-band Roofing Filter Affect Receiver Performance?

In the past, sensitivity was i of the about important receiver functioning specifications. Today, instead of sensitivity, nosotros speak of a receiver'south minimum discernible signal, or MDS. This is the weakest bespeak that a receiver will detect. One parameter that affects a receiver'due south MDS is the dissonance effigy. The dissonance figure of a receiver is the ratio in dB of the noise generated by the receiver compared to the theoretical minimum dissonance.

QUESTION: What does the MDS of a receiver represent? (E4C07)
ANSWER: The minimum discernible signal

QUESTION: What is the noise effigy of a receiver? (E4C04)
ANSWER: The ratio in dB of the noise generated by the receiver to the theoretical minimum noise

A related specification is the noise floor. A racket floor of -174 dBm/Hz, is the theoretical racket at the input of a perfect receiver at room temperature. If a CW receiver with the AGC off has an equivalent input dissonance power density of -174 dBm/Hz, the level of an unmodulated carrier input to this receiver would accept to be -148 dBm to yield an audio output SNR of 0 dB in a 400 Hz noise bandwidth.

QUESTION: What does a receiver noise floor of -174 dBm correspond? (E4C05)
ANSWER: The theoretical racket in a one Hz bandwidth at the input of a perfect receiver at room temperature

QUESTION: A CW receiver with the AGC off has an equivalent input noise ability density of -174 dBm/Hz. What would exist the level of an unmodulated carrier input to this receiver that would yield an sound output SNR of 0 dB in a 400 Hz dissonance bandwidth? (E4C06)
Respond: -148 dBm

Mod transceivers use digital signal processing (DSP) to filter out dissonance and eliminate interference at one of the IF stages. Instead of merely a few stock-still bandwidths, DSP techniques allow an operator to select from a wide multifariousness of bandwidths, enabling the operator to select a receive bandwidth that's optimum for the type of signal he or she is receiving. This maximizes the signal to noise ration and minimizes interference.

QUESTION: What is an reward of having a variety of receiver IF bandwidths from which to select? (E4C10)
Reply: Receive bandwidth tin can be set to match the modulation bandwidth, maximizing bespeak-to-noise ratio and minimizing interference

Although modern transceivers take sophisticated DSP filters, many likewise employ covering filters to improve receiver functioning. Roofing filters filter incoming signals before the first intermediate frequency (IF) phase, blocking strong signals near the receive frequency that could cause overloading and distortion in the following amplifier stages. In doing so, a narrow-band covering filter improves a receiver's dynamic range.

QUESTION: How does a narrow-ring roofing filter bear on receiver operation? (E4C13)
Reply: It improves dynamic range by attenuating strong signals near the receive frequency

Back in the twenty-four hours, when superheterodyne receivers had intermediate frequencies in the 400 – 500 kHz range, image rejection was a problem. If there was a strong signal nowadays on a frequency about 2 times the IF away from the receive frequency, you lot might hear that signal. For example, you might hear a strong signal transmitting on fifteen.210 MHz on a receiver that has a 455 kHz IF frequency and is tuned to xiv.300 MHz.

QUESTION: What transmit frequency might generate an image response signal in a receiver tuned to 14.300 MHz and that uses a 455 kHz IF frequency? (E4C14)
Respond: 15.210 MHz

I solution to this problem is to select a higher IF frequency. Doing so makes it easier for front-end circuitry, such as IF filters, to eliminate image responses. A front end-end filter or pre-selector of a receiver can also be effective in eliminating image signal interference.

QUESTION: Which of the following choices is a skilful reason for selecting a high frequency for the blueprint of the IF in a superheterodyne HF or VHF communications receiver? (E4C09)
ANSWER: Easier for front-end circuitry to eliminate paradigm responses

QUESTION: Which of the post-obit receiver circuits can be effective in eliminating interference from strong out-of-band signals? (E4C02)
Respond: A front-cease filter or pre-selector

Because most mod transceivers apply digital techniques to generate a local oscillator betoken to tune a receiver, synthesizer stage dissonance might be a trouble. An result of excessive phase dissonance in the local oscillator section of a receiver is that it can combine with strong signals on nearby frequencies to generate interference. The procedure whereby local oscillator phase noise combines with adjacent strong signals to create interference to desired signals is called reciprocal mixing.

QUESTION: What is an effect of excessive stage dissonance in a receiver'due south local oscillator? (E4C01)
Reply: It can combine with strong signals on nearby frequencies to generate interference

QUESTION: What is reciprocal mixing? (E4C15)
ANSWER: Local oscillator phase racket mixing with adjacent strong signals to create interference to desired signals

Software-defined radio (SDR) is becoming more popular in amateur radio. It is, therefore, necessary to know something well-nigh SDR receiver characteristics. For example, an SDR receiver'due south analog-to-digital converter (ADC) sample width in $.25 has the largest effect on an SDR receiver's linearity. An SDR receiver is overloaded when input signals exceeds the reference voltage of the analog-to-digital converter. When this happens, the ADC outputs the maximum value no matter what the input value is.

QUESTION: Which of the following has the largest effect on an SDR receiver's dynamic range? (E4C12)
ANSWER: Analog-to-digital converter sample width in $.25

QUESTION: An SDR receiver is overloaded when input signals exceed what level? (E4C08)
Answer: The reference voltage of the analog-to-digital converter

Most transceivers take built-in attenuators to reduce receiver overload. Although attenuators reduce the forcefulness of incoming signals, they accept little or no impact on indicate-to-racket ratio because atmospheric noise is a much bigger contributor to the overall noise level than internally generated noise, and the attenuator attenuates atmospheric noise as much as information technology does the incoming point.

QUESTION: Why tin can an attenuator be used to reduce receiver overload on the lower frequency HF bands with little or no touch on signal-to-noise ratio? (E4C11)
Answer: Atmospheric racket is generally greater than internally generated noise fifty-fifty after attenuation

Finally, here is a miscellaneous question on FM receiver performance characteristics.

QUESTION: What is the term for the suppression in an FM receiver of 1 signal by another stronger point on the same frequency? (E4C03)
ANSWER: Capture upshot

How Does A Narrow-band Roofing Filter Affect Receiver Performance?,

Source: https://www.kb6nu.com/2020-extra-class-study-guide-e4c-receiver-performance-characteristics-phase-noise-noise-floor-image-rejection-mds-signal-to-noise-ratio-noise-figure-reciprocal-mixing-selectivity-e/#:~:text=Roofing%20filters%20filter%20incoming%20signals,improves%20a%20receiver's%20dynamic%20range.

Posted by: schmidttheran.blogspot.com

Share this post